Method and bath for electroplating tin

ABSTRACT

AN AQUEOUS BATH FOR ELECTROPLATING TIN UPON VARIOUS CONDUCTIVE SUBSTRATES CONTAINS STAMNOUS ION, SULFATE RADICAL, AN IMIDAZOLINE DERIVATIE AND A HETEROCYCLIC ALDEHYDE. THE BATH IS HIGHLY ACID AND IS OPERABLE TO PRODUCE SMOOTH ADHERENT DEPOSITS OVER A WIDE RANGE OF CURRENT DENSITIES AND DEPOSITS OF SPECTRAL BRIGHTNESS WITH THE OPTIMUM FORMULATIONS.

United States Patent O 3,577,328 METHOD AND BATH FOR ELECTROPLATING TIN George B. Rynne, Rockville, and Merton M. Beckwith,

Tolland, Conn., assignors to Conversion Chemical Corporation, Rockville, Conn. N Drawing. Filed Nov. 7, 1968, Ser. No. 774,177 Int. Cl. C23b 5/46 US. Cl. 204-54 25 Claims ABSTRACT OF THE DISCLOSURE An aqueous bath for electroplating tin upon various conductive substrates contains stannous ion, sulfate radical, an irnidazoline derivative and a heterocyclic aldehyde. The bath is highly acid and is operable to produce smooth adherent deposits over a wide range of current densities and deposits of spectral brightness with the optimum formulations.

BACKGROUND OF THE INVENTION A variety of baths have been employed for electrodepositing tin upon metallic substrates, possibly the most widely used of which are the stannous fluoborate and caustic stannate solutions. Although these prior art baths have proven generally satisfactory and have been widely utilized, they are usually deficient in one or more desirable operating characteristics, and the deposits which they produce frequently fail to provide a desirable balance of brightness, smoothness, ductility, adherence, solderability, porosity and stability against ageing. Some of the baths are relatively expensive and many tend to be difiicult to maintain since fairly critical control of the concentrations of the components thereof is normally required. Recent efforts to provide bright tin deposits are described by P. Baeyens and G. Krijl in Philips Formaldehyde Bright Tin, in Transactions of the Institute of Metal Finishing, 1967, volume 45, at pages 115-121, and in Korpiun et al. US. Letters Pat. No. 3,361,562.

Although various of the baths which have been described in the literature and in the patents are operable with varying degrees of efficiency and effectiveness, there has, nevertheless, remained a need to develop a bath capable of producing smooth adherent deposits which exhibit spectral brightness and in which there is considerable stability of the components. Moreover, there has been a continuing need to provide baths which are relatively economical in that the primary and secondary brightners or surface active agents are not excessively consumed.

Accordingly, it is an objeht of the present invention to provide a bath for producing smooth, adherent and relatively nonporous deposits of tin which can range from bright to spectral bright.

It is also an object to provide such a bath which is relatively inexpensive and convenient to maintain and which does not require a high level of control of the concentration of the components thereof within critical limits.

Another object is to provide such a bath for electrodepositing tin at suitable operating rates which is operable over a broad range of current densities to provide deposits of spectral brightness.

A specific object is to provide a convenient and relatively rapid method for electroplating tin upon metallic workpieces utilizing an improved sulfate plating bath to obtain highly desirable tin deposits at relatively low cost.

SUMMARY OF THE INVENTION It has now been found that the foregoing and related objects can be readily attained in an aqueous bath containing about 10.0 to 50.0 grams per liter of stannous ion, about 100.0 to 250.0 grams per liter of sulfate radical,

ice

about 0.2 to 20.0 grams per liter of a surface active agent selected from the group consisting of irnidazoline derivatives and mixtures of irnidazoline derivatives with condensates of an alkyl phenol having an alkyl chain of 6.to 12 carbon atoms with an alkylene oxide selected from the class consisting of ethylene oxide, propylene oxide and mixtures thereof, and 0.005 to 1.0 gram per liter of a heterocyclic aldehyde wherein the heterocyclic ring has five members and the carboxaldehyde group is attached to a carbon atom in the ring. In addition, the bath is highly acid and contains about 1.5 to 4.5 grams per liter of hydrogen ion.

The preferred baths utilize an irnidazoline derivative in combination with an alkyl phenol-alkylene oxide condensate since such a combination makes possible electrodeposits exhibiting spectral brightness over a wide range of current density. The baths are useful for still and barrel plating and are operable over a fairly wide range of current density.

The aqueous bath is prepared and maintained at a tem perture of about 45 to Fahrenheit. The workpiece which has a conductive surface and a suitable high-purity tin anode are immersed in the bath and a voltage is applied to provide a current density of about 0.5 to 150.0 amperes per square foot at the surface of the workpiece. As a result, a smooth, adherent, ductile deposit of tin is produced which may vary from bright to spectral bright depending upon the current density and whether the optimum formulation is employed for a given set of conditions, as will be pointed out more fully hereinafter;

DESCRIPTION OF THE PREFERRED EMBODIMENTS The acid baths of the present invention require the stannous ion, the sulfate radical, an irnidazoline derivative and the heterocyclic aldehyde for proper operation. The stannous ion and the sulfate radical may be furnished to the bath by any combination of compounds suitable for use in tin plating solutions, but to avoid the presence of unnecessary and possibly interfering ions, these components are desirably introduced in the form of stannous sulfate and sulphuric acid. As is apparent, the former compound vw'll provide both the stannous ion and the sulfate radical, whereas the latter compound provide additional sulfate radical which is present in the bath. The use of sulphuric acid is also desirable from the standpoint of control of the hydrogen ion concentration, although other acids providing non-interfering radicals may also be used for that purpose. Tin compounds other than stannous sulfate, e.g., stannous fluoborate, may be employed, but preferably they are used in amounts of not more than about 50 percent by weight of the sulfate compound, and preferably less than 20 percent by weight thereof.

Although the amount of stannous ion present in the baths may vary between about 10.0 and 50.0 grams per liter, it is preferably about 12.0 to 20.0 grams per liter. Similarly, although the concentration of sulfate ion may normally be between about 100.0 and 250.0, it is preferably about 175.0 to 225.0 grams per liter. Although a broad range of about 1.5 to 4.5 grams per liter is suitable for the hydrogen ion concentration, it is most desirably maintained at about 2.5 to 3.5 grams per liter. If the concentration of stannous ion in the bath is too low, the efiiciency of plating and the quality of the deposit produced will be unsatisfactory at the low current density area; burning will be apparent at the high density area. On the other hand, although high levels of this ion permit desirable deposits to be obtained at higher current densities, too high a stannous ion concentration tends to result in the formation of a very poor deposit at low current density and to minimize the benefit aiforded by the brightener system. Maintaining the sulfate radical and the hydrogen ion within the ranges of concentrations specified will ensure that the bath operates efficiently to produce the type of deposits desired.

The surface-active agent 1120-011, onzz NI CHZGHZY N=C \G In the foregoing formula, R represents an alkyl radical having to 24 carbon atoms; G is OH ion, an acid salt radical, an anionic surface-active sulfate salt radical such as preferably OSO -OR, or an anionic surface-active sulfonate salt radical; and Z is CCOM, CH COOM, or HO-CHCH SO M radical. The substituent designated M in the foregoing formula is a hydrogen atom, an alkali metal or an organic base, and that designated Y is either an OR' or N (:R') A group. Each R substituent is independently selected from the group consisting of hydrogen, alkali metals, and -(CH COOM; A represents an anionic monovalent radical and n represents an integer from 1 to 4. Use of the dotted line representation for the bonds connecting the substituents G and CH Z to the nitrogen atom indicates that these substituents are optionally present or absent, but it should be understood that they are either both present or both absent. Desirable compounds are provided when, in accordance with the foregoing formula, G represents the radical par ucularly in which R is a C to C alkyl group, and Z is a COOM radical in which M is preferably an alkali metal cation.

Exemplary of the compounds corresponding to the foregoing formula which are satisfactory for use in the baths described herein are 2-alkyl-l-(ethyl-beta-oxypropanoic acid) imidazolines wherein the alkyl group is capryl, undecyl or a mixture of C C chains, and the disodium salt of lauroyl-cycloimidinium-l-ethoxyethanoic acid 2- ethanoic acid.

Although the imidazoline derivatives provide a desirable degree of brightening when used alone, generally the full advantages of the present invention can be attained only by use of imidazoline derivatives in combination with the condensate of an alkyl phenol and alkylene oxides. The alkylene oxide willbe present in a molar ratio relative to the alkyl phenol of about 8 to 25:1 and is selected from the class consisting of ethylene oxide, propylene oxide and mixtures thereof. The alkyl substituent on the phenol has a carbonchain of 6 to 12 carbon atoms and preferably '8 to 10.

Exemplary of the alkyl phenol condensates are octyl phenoxy polyethoxy ethanols and nonyl phenoxy polyethoxy ethanols with the preferred agents being nonyl phenoxy polyethoxy ethanols having a molar ratio of about 9 to,20:1.

The total concentration of the surface-active agent may vary from about 0.2 to 20.0 grams per liter and is preferably in the range of about 1.0- to 4.0 grams per liter. As indicated above, the preferred surface-active agents are, in fact, a combination of the imidazoline derivative and the alkyl phenol condensate. Particularly beneficial results have been obtained by the use of the imidazoline in an amount of about 1.0 to 2.5 grams per liter and the alkyl phenol condensate in the amount of about 1.0 to 1.0 gram per liter.

Moreover, it has been found that the best results with the imidazoline derivatives are obtained by using combinations of such derivatives. Particularly significant benefits are obtained by a mixture of (A) an imidazoline derivative wherein the groups G and CH Z are both omitted and Y is N (CH -COOH] C1, n being equal to 1 to 4; and (B) an imidazoline derivative wherein -G is OH and wherein Y is equal to O(CH ),,COOM and wherein Z is equal to -(CH COOM, n being equal to l to 4 and m equal to 0 to 1 and M being an alkali metal. A highly beneficial system is that obtained by a mixture of an imidazoline corresponding to the aforementioned general formula wherein Z is COONa, G is OH, and Y is OCH COONa', and a second imidazoline wherein the groups G and CH Z are omitted and Y is N CH CH COOH) 2 (CH COOH) Cl The first-mentioned imidazoline derivative is provided in a weight ratio of about 1 to 8:1 relative to the secondmentioned imidazoline derivative and preferably in a ratio of about 4.5 to 6.5.

The heterocyclic carboxaldehydes The other essential component in the system is the heterocyclic carboxaldehyde which acts as a primary brightener. As indicated hereinbefore, the heterocyclic ring is five membered and may be based upon thiophene, furan and pyrrole. The carboxaldehyde group is attached to one of the carbons in the ring which generally will be in the 2-position, and the preferred compounds are those in which a simple carboxaldehyde group (CHO) is employed although longer carbon chain carboxaldehydes may also be employed; in addition, the carboxaldehydes may be ringor chain-substituted materials. Specific heterocyclic carboxaldehydes which have proved highly effective are furfural (2-furaldehyde), 2-thiophene carboxaldehyde and 2-pyrrole carboxaldehyde.

Although beneficial results have been obtained by the incorporation of heterocyclic carboxaldehydes in amounts as little as 0.005 gram per liter, the brightener is preferably included in amounts of at least 0.01 and desirably at least 0.05 gram per liter. As the amount of aldehyde is increased above about 0.5 gram per liter, there is a greater difficulty in controlling the operation of the bath. Above 1.0 gram per liter, pitting and burning become quite evident and the low current density area on a test panel no longer is bright. Accordingly, the baths preferably employ the aldehyde compounds in amounts of about 0.05 to 0.5 gram per liter.

Since some of the heterocyclic carboxaldehydes demonstrate relatively low solubility in the acid bath, it may be necessary to employ a solvent solution thereof to facilitate formation of the bath composition. Among the various solvents which may be employed, depending upon the particular aldehyde selected, are the low molecular weight alkanols (methanol, ethanol and propanol) and the low molecular weight glycol ethers (ethylene glycol monoethyl ether, etc.). Generally, the aldehyde is added to the solvent in amounts of about 1.0 to 50.0 grams per liter thereof and preferably in about 5.0 to 25.0 grams per liter, so as to obtain a stable solvent solution which may be readily dispersed in the acid bath.

Other components In addition to the components described hereinbefore, other additives may be included to modify the operation of the present bath such as auxiliary brighteners, surfaceactive agents and chelating agents. However, it has generally been found that the bath desirably operates without such additional components.

Exemplary of the auxiliary brighteners which may be added are the aryl aldehydes (benzaldehyde, cinnamaldehyde), polyvinyl alcohol and carbocyclic and heterocyclic ketones (benzylideneacetone, furylideneacetone and pyridylideneacetone). Generally, such auxiliary brighteners should be added in amounts of less than 1.0 gram per liter and preferably less than 0.2 gram per liter.

Although there has been noted no apparent tendency for the formation of metal sludge and precipitate in properly operated baths, for some applications it may be desirable to incorporate a chelating agent such as citric acid, malic acid and the aminopolyacetic acids (ethylenediamine tetraacetic acid, diethylenetriamine pentaacetic acid, and nitrilotriacetic acid. Such chelating agents, when employed, are generally included in an amount of 5.0 to 20.0 grams per liter.

Operation of the baths As has been indicated previously, the baths of the present invention are operable over a relatively wide range of cathode current density. More specifically, the operable range is about 0.5 to 150 amperes per square foot (a.s.f.) and preferably about 1 to 45 a.s.f., with a narrower range of to 30 a.s.f. being most desirable for barrel plating operations. The plating efliciency is generally quite high and will range up to about 98 percent, based upon the theoretical rate of deposition, at current densities below about amperes per square foot. In order to obtain optimum results, the anodezcathode area ratio should be about 1.0 to 3.0:1.0, and preferably about 2..0:1.0. Moreover, the anode current density should not exceed about 15 a.s.f. since there is an apparent tendency for polarization of the anode, for the brightener to become unstable and for formation of tetravalent tin. The applied voltage should be about 0.2 to 5.0 volts and preferably 0.5 to 4.0 volts.

The baths should be operated at temperatures between about 45 and 135 Fahrenheit, and preferably about 55 to 85 Fahrenheit. Operation below about 45 Fahrenheit tends to be inefiiicent and to produce undesirable deposits, whereas temperatures higher than about 135 Fahrenheit tend to produce dull, rough and generally unacceptable deposits.

Any metallic substrate or metal-surfaced article which can be plated with tin using prior art baths may be coated in accordance with the present invention. For example, good deposits of tin may be produced upon articles of copper, nickel, iron and steel. The best results are obtainable with these baths if relatively pure tin anodes are employed.

Agitation is desirable to obtain deposits which are uniform and of high quality and to avoid development of sludge or film. Not only is agitation of the bath itself desirable but agitation of the cathode may be desirable to obtain a uniform plate and to enable extension of the range of satisfactory current density to higher levels.

The process is adapted to both still plating and barrel plating apparatus with equal eflicacy. Filtration of the bath is not essential but will normally be beneficial when contamination of the bath is encountered due to airborne impurities and carryover from other finishing operations. Various filtering media may be utilized including fabric, porous stoneware and other conventional filtering materials.

The depletion of the various components of the bath is best corrected by analysis for the several components on a periodic basis which can be established for a given facility. To determine the necessity for the addition of a surface-active agent, the best procedure is to evaluate a sample of the bath in a suitable test cell, and a suitable schedule may be established for a given facility and workpiece. To determine the amounts of stannous salt required, a 0.1 N potassium iodate solution and a 1.0

Illustrative of the efiicacy of the present invention are the following specific examples wherein all parts are parts by weight unless otherwise indicated.

Example One An aqueous bath is prepared containing 30.0 grams per liter of stannous sulfate, 108.0 milliliters per liter of sulphuric acid (specific gravity 1.84), 0.6 gram per liter of an imidazoline derivative wherein groups G and CH Z are omitted and Y is N(CH CH COOH) 2 (CH COOH) Cl 0.1 gram per liter of an imidazoline derivative wherein Z is COONa, G is OH, and Y is OCH COONa, and 0.25 gram per liter of an ethylene oxide/octyl phenol condensate having a molar ratio of about 10.0:1.0, and 0.08 gram per liter of thiophene aldehyde. The bath was introduced into a barrel plating apparatus and maintained at a temperature of about 68 Fahrenheit.

Into the bath were introduced small integrated circuit packages fabricated of a ferrous alloy containing cobalt, nickel and manganese. The packages had a length of about inch and a cross-section of about /2 inch by /2 inch. A pure tin anode providing an anode to cathode ratio of about 1.011.0' was utilized and a potential of 2 volts was applied across the plating barrel with a current of about 25.0 amperes. The average cathode current density was estimated at about 7.5 a.s.f. because of the complexity of the part.

After about 12 /2 minutes the printed circuit packages were removed from the bath and were found to have an electroplated tin deposit of about 0.3 mil. The deposit was spectral bright in all current density areas of the parts and was free from burning. The deposit was also found to be highly adherent.

Example Two The procedure of Example One was substantially repeated utilizing transistors with wire leads. The cathode current density was calculated to average about 15 a.s.f. Upon removal from the bath, the transistors and the wire leads were found to be plated with a spectral bright tin deposit of about 0.3 mil thickness. Flexing of the leads did not produce any evidence of cracking of the plated deposit or of lack of adherence of the deposit to the substrate.

Example Three The procedure of Example One was again repeated utilizing as the parts being treated sheet metal and wood screw fasteners fabricated from a steel alloy. The average cathode current density was calculated at about 15 a.s.f. and the parts were found to have a spectral bright, adherent tin deposit of about 0.3 mil. thickness over their entire surface area.

Example Four In a rack plating tank were placed bearings fabricated of steel with a bonded aluminum backing. The bath in this instance was maintained at a temperature of about 60 Fahrenheit and the current applied across the tank was calculated to produce an average cathode current density of about 25 a.s.f. After 12 minutes, the parts were removed and were found to have a spectral bright tin deposit of about 0.5 mil thickness. The deposit was ductile and highly adherent to the steel portion of the bearings although adherence to the aluminum backing was typically poor as can be anticipated for an electroplated tin deposit on aluminum.

Example Five The procedure of Example Four was repeated utilizing printed circuit boards fabricated of copper with a screened resist pattern. The temperature of the bath was maintained at about 68 Fahrenheit and the cathode current density was calculated to average 15 a.s.f. After 11.5 minutes, the parts were removed from the bath and found to have a spectral bright, highly adherent tin deposit of about 0.3 mil thickness over the resist-free areas.

Example Six Part A.The bath of Example One was tested in a rotary test cell manufactured by Conversion Chemical Corporation of Rockville, Conn. in accordance with US. Letters Pat. No. 3,215,609. The test panels were cleaned steel and the potential applied across the cell was 1.0 volt developing an amperage of about 1.5. The temperature was maintained at about 68 Fahrenheit and after plating for 6 minutes, the test panels were removed and found to be bright over the entire range of about 0.5 to 100.0 amperes per square foot.

Part B.-The procedure was repeated substituting for the thiophene aldehyde an equal amount of pyrrole aldehyde. Again, the test panels were found to be spectral bright throughout the current density range of about 5.0 to 100.0 a.s.f., but a slight fogginess tending to reduce the otherwise brilliant luster was apparent in the area below about 5.0 a.s.f.

Part C.--The procedure was again repeated substituting furfural for the thiophene aldehyde. Again, the test panels were bright over the plating range of 0.5 to 100.0 amperes per square foot but a slight fog in the entire plating range tended to reduce the otherwise brilliant luster.

Example Seven The procedure of Example Six, Part A, was repeated omitting the ethylene oxide/octyl phenol condensate. In this instance, the test panels were found to have a spectral bright tin deposit in the range of about 25.0 to 100.0 a.s.f. Below about 25.0 a.s.f., there were portions of the test panels which were unplated indicating a tendency toward skip plating in the lower current density areas. However, the plated deposits were spectral bright. This and related tests indicate the very significant benefits to be obtained by combining the imidazoline derivatives with the alkyl phenol/alkylene oxide condensates.

Example Eight The procedure of Example Six, Part A, was repeated omitting from the bath the second-mentioned imidazoline derivative. In this instance, the plated deposit was uniform and adherent throughout the current density range of about 1.0 to 100.0 a.s.f. Although the deposit was bright or non-matte in character, it was not so spectral bright as that obtained by the combination of the imidazoline derivatives in the preferred bath of Example One.

Example Nine The procedure of Example Six, Part A, was repeated utilizing a standard Hull cell. The temperature of the bath was maintained at about 90 Fahrenheit and a voltage of about 3.0 was applied across the cell. After plating for about 3.0 minutes, the test panels were found to have a spectral bright, adherent tin deposit over a range of about 25.0 to 135.0 a.s.f.

Thus, it can be seen that the present invention provides a novel and highly efiective bath for electroplating tin on various metallic substrates. The deposits are adherent and ductile and may vary from bright to spectral bright depending upon whether the optimum formulations are employed. Various types of parts may be readily plated over a relatively wide range of current density.

Having thus described the invention, we claim:

1. An aqueous acid bath for producing an adherent electroplated tin deposit comprising about 10.0 to 50.0 grams per liter of stannous ion; about 100.0 to 250.0 grams per liter of sulfate radical; about 0.2 to 20.0 grams per liter of a surface active agent selected from the group consisting of imidazoline derivatives and mixtures of imidazoline derivatives with condensates of an alkyl phenol having an alkyl chain of 6 to 12 carbon atoms with an alkylene oxide selected from the class consisting of ethylene oxide, propylene oxide, and mixtures thereof; 0.005 to 1.0 gram per liter of a heterocyclic carboxaldehyde wherein the heterocyclic ring has five members and the carboxaldehyde group is attached to a carbon atom on said ring; and about 1.5 to 4.5 grams per liter of hydrogen ion.

2. The bath of claim 1 wherein the imidazoline derivative corresponds to the formula:

wherein:

(1) R" is an alkyl radical having 5 to 24 carbon atoms;

(2) G is a radical selected from the group consisting of OH, acid salt radicals, anionic surface active sulfate salt radicals, and anionic surface active sulfonate salt radicals;

(3) Z is a radical selected from the group consisting of -COOM, CH COOM, and

(4) M is a substituent selected from the group consisting of hydrogen, alkali metals and organic bases;

(5) Y is selected from the group consisting of OR and --N(R') A;

(6) each R substituent is independently selected from the group consisting of hydrogen, alkali metals, and --(CH COOM;

(7) A is an anionic monovalent radical;

(8) n is an integer from 1 to 4; and

(9) both the groups G and CH Z are present or absent.

3. The bath of claim 1 wherein said imidazoline derivative is selected from the group consisting of 2-alkyl-l- (ethyl-beta-oxypropanoic acid)-imidazolines wherein the alkyl group is selected from the class consisting of capryl, undecyl and mixtures of C7-C17 chains, and the disodium salt of lauroyl-cyclo-imidinium-l-ethoxy-ethanoic acid-2- ethanoic acid.

4. The bath of claim 1 wherein said surface active agent comprises 1.0 to 2.5 grams per liter of an imidazoline derivative and 0.1 to 1.0 gram per liter of an alkyl phenol condensate.

5. The bath of claim 1 wherein the stannous ion concentration is about 12.0 to 20.0 grams per liter, the sulfate radical concentration is about 175.0 to 225.0 grams per liter, the surface active agent concentration is about 1.0 to 4.0 grams per liter and the heterocyclic aldehyde concentration is about 0.0 5 to 0.5 gram per liter.

6. The bath of claim 1 wherein at least the predominant portion of said stannous ion is provided by stannous sulfate and wherein at least a portion of said sulfate radical is furnished by sulphuric acid.

7. The bath of claim 1 wherein said carboxaldehyde group has the structure CHO.

8. An aqueous acid bath for producing an adherent electroplated tin deposit comprising about 10.0 to 50.0 grams per liter of stannous ion; about 100.0 to 250.0 grams per liter of sulfate radical; about 0.2 to 20.0 grams per liter of a surface active agent selected from the group consisting of imidazoline derivatives and mixtures of imidazoline derivatives with condensates of an alkyl phenol having an alkyl chain of 6 to 12 carbon atoms with an alkylene oxide selected from the class consisting of ethylene oxide, propylene oxide, and mixtures thereof; 0.005 to 1.0 gram per liter of an heterocyclic carboxaldehyde wherein the heterocyclic ring has five members and the carboxaldehyde group is attached to a carbon atom on said ring; and about 1.5 to 4.5 grams per liter of hydrogen ion, said imidazoline derivative corresponding to the formula:

HzC-CHz CHzCO OM N-CHzCHzY N=C OSOzOR wherein:

R is an alkyl radical having 10 to 18 carbon atoms, M is an alkali metal cation, Y is selected from the group consisting of OR' and N(R') A, each R substituent is independently selected from the group consisting of hydrogen, alkali metals, and

R" is an alkyl radical having 5 to 24 carbon atoms, A is an anionic monovalent radical and n is an integer from 1 to 4.

9. An aqueous acid bath for producing an adherent electroplated tin deposit comprising about 10.0 to 50.0 grams per liter of stannous ion; about 100.0 to 250.0 grams per liter of sulfate radical; about 0.2 to 20.0 grams per liter of a surface active agent selected from the group consisting of both imidazoline derivatives (A) and (B) and mixtures of both imidazoline derivatives (A) and (B) with condensates of an alkyl phenol having an alkyl chain of 6 to 12 carbon atoms with an alkylene oxide selected from the class consisting of ethylene oxide, propylene oxide, and mixtures thereof; 0.005 to l/O gram per liter of a heterocyclic carboxaldehyde wherein the heterocyclic ring has five members and the carboxaldehyde group is attached to a carbon atom on said ring; and about 1.5 to 4.5 grams per liter of hydrogen ion, each of said imidazoline derivatives (A) and (B) corresponding to the formula Ego-CH2 CH2(CH2)mCOOM Ni-omoniY N=o H I LII wherein R" is an alkyl radical having to 24 carbon atoms, M is an alkali metal, Y is selected from the group consisting of O(CH COOM and n is an integer from 1 to 4, and both of the optional groups -OH and CH (CH2) COOM are present or absent; in said imidazoline derivative (A) said optional groups are both absent and Y is N[(CH -COOH] Cl, and in said imidazoline derivative (B) said optional groups are present, Y is O(CH ),,COOM, and m is 0 to l.

10. The bath of claim 9 wherein imidazoline derivative (A) is present in a weight ratio relative to imidazoline derivative (B) of about 1.0 to 8.0: 1.0.

11. The bath of claim 10 wherein said surface-active agent contains both the imidazoline derivatives and the alkyl phenol condensate, the imidazoline derivatives being present in an amount of about 1.0 to 2.5 grams per liter and the condensate being present in an amount of about 0.1 to 1.0 gram per liter.

12. The bath of claim 11 wherein the stannous ion concentration is about 12.0 to 20.0 grams per liter, the sulfate radical concentration is about 175.0 to 225.0 grams per liter, the surface active agent concentration is about 1.0 to 4.0 grams per liter and the heterocyclic aldehyde concentration is about 0.05 to 0.5 gram per liter.

13. In a method for electroplating tin, the steps comprising:

(1) preparing an aqueous acid bath comprising about 10.0 to 50.0 grams per liter of stannous ion; about 100.0 to 250.0 grams per liter of sulfate radical; about 0.2 to 20.0 grams per liter of a surface-active agent selected from the group consisting of imidazoline derivatives and mixtures of imidazoline derivatives with condensates of an alkyl phenol having an 10 alkyl chain of 6 to 12 carbon atoms with an alkylene oxide selected from the class consisting of ethylene oxide, propylene oxide, and mixtures thereof; about 1.5 to 4.5 grams per liter of hydrogen ion; and about 0.005 to 1.0 gram per liter of a heterocyclic carboxaldehyde wherein the heterocyclic ring has five members and the carboxaldehyde group is attached to a carbon atom in said ring;

(2) maintaining said bath at a temperature of about 45 to Fahrenheit;

(3) immersing a workpiece having a metallic surface and a tin anode in said bath; and

(4) applying a voltage across said anode and workpiece to deposit tin on said metallic surface, said voltage providing a current density of about 0.5 to amperes per square foot at the workpiece.

14. The method of claim 13 wherein the imidazoline derivative corresponds to the formula:

( 1) R" is an alkyl radical having 5 to 24 carbon atoms;

(2) G is a radical selected from the group consisting of -OH, acid salt radicals, anionic surface-active sulfate salt radicals, and anionic surface-active sulfonate salt radicals;

(3) Z is a radical selected from the group consisting of COOM, CH COOM, and HO-CH--CH SO M;

(4) M is a substituent selected from the group consisting of hydrogen, alkali metals and organic bases;

(5) Y is selected from the group consisting of OR' and N(R') A;

(6) each R substituent is independently selected from the group consisting of hydrogen, alkali metals, and --(CH COOM;

(7) A is an anionic monovalent radical;

(8) n is an integer from 1 to 4; and

(9) both the groups G and CH Z are present or absent.

15. The method of claim 13 said surface-active agent comprises 1.0 to 2.5 grams per liter of an imidazoline derivative and 0.1 to 1.0 gram per liter of an alkyl phenol condensate.

16. The method of claim 13 wherein the stannous ion concentration is about 12.0 to 20.0 grams per liter, the sulfate radical concentration is about 175.0 to 225.0 grams per liter, the surface-active agent concentration is about 1.0 to 4.0 grams per liter and the heterocyclic aldehyde concentration is about 0.05 to 0.5 gram per liter.

17. The method of claim 13 wherein said imidazoline derivative is selected from the group consisting of 2-alkyl- 1-(ethyl-beta-oxypropanoic acid)-imidazolines wherein the alkyl group is selected from the class consisting of capryl, undecyl and mixtures of C -C chains, and the disodium salt of lauroyl-cyclo-imidinium-l-ethoxy-ethanoic acid 2-ethanoic acid.

18. The method of claim 13 wherein said carboxaldehyde group has the structure CHO.

19. The method of claim 13 wherein at least the predominant portion of said stannous ion is provided by stannous sulfate and wherein at least a portion of said sulfate radical is furnished by sulphuric acid.

20. The method of claim 13 wherein said voltage applied provides a current density of about 1 to 45 amperes per square foot of workpiece and wherein said temperature is maintained at about 55 to 85 Fahrenheit.

21. In a method for electroplating tin, the steps comprising:

(1) preparing an aqueous acid bath comprising about n 10.0 to 50.0 grams per liter of stannous ion; about 100.0 to 250.0 grams per liter of sulfate radical;

about 0.2 to 20.0 grams per liter of a surface-active agent selected from the group consisting of imidazoline derivatives and mixtures of imidazoline derivatives with condensates of an alkyl phenol having an alkyl chain of 6 to 12 carbon atoms with an alkylene oxide selected from the class consisting of ethylene oxide, propylene oxide, and mixtures thereof; about 1.5 to 4.5 grams per liter of hydrogen ion; and about 0.005 to 1.0 gram per liter of a heterocyclic carboxaldehyde wherein the heterocyclic ring has five members and the carboxaldehyde group is attached to a carbon atom in said ring; said imidazoline derivative corresponding to the formula:

wherein R is an alkyl radical having to 18 carbon atoms, M is an alkali metal cation, Y is selected from the group consisting of OR' and N(R) A, each R substituent is independently selected from the group consisting of hydrogen, alkali metals, and -(CH COOM, R" is an alkyl radical having 5 to 24 carbon atoms, A is an anionic monovalent radical and n is an integer from 1 to 4;

(2) maintaining said bath at a temperature of about 45 to 135 Fahrenheit;

(3) immersing a workpiece having a metallic surface and a tin anode in said bath; and

(4) appying a voltage across said anode and workpiece to deposit tin on said metallic surface, said voltage providing a current density of about 0.5 to 150 amperes per square foot at the workpiece.

22. In a method for electroplating tin, the steps comprising:

(1) preparing an aqueous acid bath comprising about 10.0 to 50.0 grams per liter of stannous ion; about 100.0 to 250.0 grams per liter of sulfate radical; about 0.2 to 20.0 grams per liter of a surface-active agent selected from the group consisting of both imidazoline derivatives (A) and (B) and mixtures of both imidazoline derivatives (A) and (B) with condensates of an alkyl phenol having an alkyl chain of 6 to 12 carbon atoms with an alkylene oxide selected from the class consisting of ethylene oxide, propylene oxide, and mixtures thereof; about 1.5 to 4.5 grams per liter of hydrogen ion; and about 0.005 to 1.0 gram per liter of heterocyclic carboxaldehyde wherein the heterocyclic ring has five members and the carboxaldehyde group is attached to acarbon 12 atom in said ring, each of said imidazoline derivatives (A) and (B) corresponding to the formula wherein R" is an alkyl radical having 5 to 24 carbon atoms, M is an alkali metal, Y is selected from the group consisting of -O(CH COOM and n is an integer from 1 to 4, and both of the optional groups --OH and -CH (CH COOM are present or absent; in said imidazoline derivative (A) said optional groups are both absent and Y is and in said imidazoline derivative (B) said optional groups are present, Y is -O(CH COOM, and m is 0 to 1;

(2) maintaining said bath at a temperature of about 45 to Fahrenheit;

(3) immersing a workpiece having a metallic surface and a tin anode in said bath; and

(4) applying a voltage across said anode and workpiece to deposit tin on said metallic surface, said voltage providing a current density of about 0.5 to amperes per square foot at the workpiece.

23. The method of claim 22 wherein imidazoline derivative (A) is present in a weight ratio relative to imidazoline derivative (B) of about 1.0 to 8.0:1.0.

24. The method of claim 23 wherein said surface-active agent contains both the imidazoline derivatives and the alkyl phenol condensate, the imidazoline derivatives being present in an amount of about 1.0 to 2.5 grams per liter and the condensate being present in an amount of about 0.1 to 1.0 gram per liter.

25. The method of claim 24 wherein the stannous ion concentration is about 12.0 to 20.0 grams per liter, the sulfate radical concentration is about 175.0 to 225.0 grams per liter, the surface-active agent concentration is about 1.0 to 4.0 grams per liter and the heterocyclic aldehyde concentration is about 0.05 to 0.5 grams per liter.

References Cited UNITED STATES PATENTS 3,361,652 1/1968 Korpiun et a1 204--54 JOHN H. MACK, Primary Examiner R. L. ANDREWS, Assistant Examiner 

